1. Field of the Invention
The present invention pertains to the art of conveyorized microwave ovens and, more particularly, to a shielding system provided to protect select portions of a food item directed through a microwave oven on a conveyor from high intensity microwaves.
2. Discussion of the Prior Art
Conveyorized microwave ovens have been used for years in industrial and commercial cooking applications. In many cases, pre-packaged food items having a defined shape are passed through the oven during processing. Many of the packages and food items are in the form of parallelepipeds which have a plurality of corners or generally sharp projections. While the shape of the package or food item lends itself to convienent handling and storage, it can create a problem during the cooking process. More specifically, corners or sharp projections tend to magnify the microwave field, thereby creating localized hot spots within the food item. The localized hot spots result in uneven cooking, burning and even food spoilage. For instance, if a localized hot spot is created when it is desired to temper or thaw a food item, the food item may be heated beyond a desired level, thus essentially destroying the product.
In connection with microwave cooking in general, several methods have been proposed to shield the corners of food items being cooked. One example is close wrapping metal or aluminum foil over the edges of the food item. This is neither convenient nor cost effective, particularly for commercial, conveyorized microwave cooking systems. Other examples include placing a food item in special container designed to protect edges of the food item from exposure to the microwave energy. However, this proposal is also not considered reasonably feasible in connection with a continuous or substantially continuous microwave cooking system.
Based on the above, there exists a need in the art for a shielding system for a conveyorized microwave cooking process, particularly a shielding system capable of protecting corners, edges or sharp projections of a food item from direct exposure to the microwave energy field as the food item passes through a microwave cooking oven on a conveyor.
The present invention is directed to a conveyorized microwave oven which incorporates a shielding system designed to assure more even cooking for a food item traveling through the microwave oven. More particularly, the shielding system constitutes specific structure mounted within a cooking cavity of the microwave oven which prevents corners or edge portions of a parallelepiped-shaped food item traveling through the microwave oven from being excessively cooked relative to the remainder of the food item. In accordance with the most preferred form of the invention, the shielding system constitutes frame structure which traverses substantially the entire length of the cooking cavity, with the frame structure being formed from a microwave impermeable material that extends about the edge portions of the conveyor supported food items.
In a preferred form of the invention. the microwave impermeable portions of the frame structure are formed from metal, although other materials impermeable to microwave energy could be employed. The frame structure includes a plurality of sections which are preferably spaced from each other so as to define microwave transmissive zones which allow microwave energy to enter the center of the frame structure where the food item is located on the conveyor belt. The overall shielding system is specifically configured according to the shape and dimensions of the particular food item to be cooked. As the food items are moving through the shielding system, a clearance is maintained between the frame structure and the food item. In accordance with the invention, the clearance between the food item and the frame structure is preferably configured be less than xc2xcxcex of the microwave energy.
When cooking food items in the microwave oven of the invention, food items are directed into the shielding system within the oven cavity upon the conveyor. The shielding system extends longitudinally within the oven cavity and is open at both ends. In this manner, predetermined portions of the food items are shielded from at least the full force of the microwave energy field during the cooking process. Most preferably, in addition to acting as a shield, the frame structure functions as a scatterer to effectively mix microwave modes and create surface waves that move along food item surfaces, thereby lessening the concentration of microwaves at the corners or edges of the food item.
Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of a preferred embodiment when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.